Certain processes require application of a coating over features that are not planar. One such process in the electronics manufacturing industry is the application of protective coating over metallic conductors that exist on an insulating planar substrate. These conductors may have various shapes, their height-to-width aspect ratio may be very small or very large, and their absolute height above the plane may substantially vary from place to place. Yet, there usually is a requirement to cover certain parts of the substrate and certain parts of the metallic portions above the plane with an even coating of a pre-specified thickness.
Inkjet printing has inherent deficiency in covering vertical portions protruding above the plane. In vertical or steep portions, the ink may flow and result in a coating with thickness that is below the required amount or result in a totally uncoated area.
For example, during the electronic printed circuit board (PCB) manufacturing process, a planar substrate (laminate) having conducting traces which usually consist of copper with varying thicknesses across the PCB has to be covered with a layer of solder mask over certain portions of the PCB. The purpose of the solder mask is to create a protective layer over the conductors and to enable soldering in the required areas (pads, etc) by leaving them uncoated. The solder mask is printed on the laminate and on the copper conductors that are higher than the laminate and is expected to cover the copper conductors with even thickness in order to withstand erosion during the manufacturing processes that follow, due to the aggressive chemicals applied.
There is a growing need to provide efficient processes for printing an even coating regardless of the 3D profile of the printed surface.